1. Field of the Invention
The present invention relates to a battery voltage measurement device for measuring a voltage of stacked rechargeable batteries (a battery pack) which is mounted in an apparatus driven by the rechargeable batteries, such as an electric vehicle or the like.
2. Description of the Related Art
As a low-pollution vehicle designed for the purpose of solving environmental problems and energy problems, an electric vehicle such as an HEV (hybrid electric vehicle) and a PEV (pure electric vehicle) has received a great deal of attention up to the present. The electric vehicle has rechargeable batteries mounted therein, and the electric power of the rechargeable batteries drives an electric motor so as to run the electric vehicle. The electric vehicle has a high-voltage circuit for driving the electric motor and a low-voltage circuit for driving various electronic devices such as acoustic equipment, lighting devices, and an electronic controller (e.g., ECU; electronic control unit). The high-voltage circuit includes an inverter for driving an electric motor, and the inverter controls and drives the electric motor.
In a battery control section of such an electric vehicle, in order to obtain an output state of the rechargeable batteries which stably supplies electric power to the electric motor, it is necessary to use a battery voltage measurement device to accurately measure a battery voltage of each battery block of the battery pack.
FIG. 5 is a circuit diagram illustrating an exemplary structure of a conventional battery voltage measurement device 100. In FIG. 5, the battery voltage measurement device 100 includes: a plurality of switches 120 in which each pair of adjacent switches 120 sequentially selects two corresponding output terminals 111a of a battery block 111 included in a battery pack 110; a capacitor 130 for storing (copying) a designated battery voltage; switches 140 for selectively applying the battery voltage stored in the capacitor 130 to a differential amplifier 150; the differential amplifier 150 for differentially amplifying the stored battery voltage which is input thereto via the switches 140; and an A/D converter 160 for performing an A/D conversion of the voltage output from the differential amplifier 150.
The battery pack 110 includes a plurality of serially-connected battery blocks 111. A value of a voltage output from one battery block 111 (battery module) is, for example, about DC 20 V. The maximum value of a voltage output from all of the serially-stacked battery blocks 111 is about DC 400 V.
Each pair of adjacent switches 120 is connected to the two corresponding output terminals 111a of each of the plurality of battery blocks 111.
The capacitor 130 has electrodes connected to a pair of conductor lines 141a and 141b laid between the switches 120 and the switches 140. The capacitor 130 temporarily stores a battery voltage of each of the battery blocks 111, which is transferred via two designated switches 120 to the capacitor 130.
Each of the switches 140 is connected to one of the two input terminals of the differential amplifier 150 and serves to connect the differential amplifier 150 to the capacitor 130 or disconnect the differential amplifier 150 from the capacitor 130. On/Off control of the plurality of switches 120 and the switches 140 is performed by a switching controller (not shown), e.g., a microcomputer.
With the above-described structure, at first, in order to store (copy) a battery voltage of a first battery block 111 in (into) the capacitor 130, each of the switches 120 connected to one of the two output terminals 111a of the first battery block 111 is turned on. At this time, the switches 140 are turned off to disconnect the capacitor 130 from both of the two input terminals of the differential amplifier 150.
Next, all the switches 120 are turned off to disconnect the capacitor 130 from all of the battery blocks 111, and then the switches 140 are turned on so as to input the battery voltage of the first battery block 111, which is stored in the capacitor 130, to the differential amplifier 150 for a gain adjustment. The battery voltage, e.g., DC 20 V, is differentially amplified by the differential amplifier 150 so as to be DC 5 V, which is in an input voltage range (dynamic range) of the A/D converter 160. The A/D converter 160 performs an A/D conversion of battery voltage data corresponding to the differentially-amplified battery voltage. The A/D-converted battery voltage data can be read by, for example, a microcomputer (not shown) in a subsequent stage.
In a similar manner, a battery voltage of the second battery block 111 is stored in (copied into) the capacitor 130. The battery voltage stored in the capacitor 130 which is derived from the second battery block 111 has an inverted polarity to that derived from the first battery block. The battery voltage of the second battery block 111, which is stored in the capacitor 130, is differentially amplified by the differential amplifier 150, and then the A/D converter 160 performs an A/D conversion of the differentially-amplified battery voltage.
Referring to FIGS. 6A, 6B, 7A, 7B, 8A, and 8B, the differential amplifier 150 and the A/D converter 160 are described in more detail below.
In general, when an analog input voltage is arithmetically processed in a CPU (central processing unit), a voltage value conversion circuit and an A/D converter are used.
The voltage value conversion circuit includes an analog circuit for performing division when an input voltage is high and performing multiplication when the input voltage is low (the analog circuit also performs addition and subtraction in addition to division and multiplication). The analog circuit is realized by a voltage divider circuit including a resistance, a circuit using an operational amplifier, and the like. A conversion result produced by the voltage value conversion circuit corresponds to an input voltage range of an A/D converter. The input voltage range of the A/D converter is, for example, between GND (0 V) and DC 5 V.
The A/D converter is a component for comparing an input voltage (e.g., a battery voltage output from the voltage value conversion circuit) with a reference voltage to convert the input voltage into digital data which can be read by a microcomputer. The performance of an A/D converter is generally determined according to the fineness of comparison in view of resolution rather than conversion accuracy although it is important for comparing voltages. The fineness of comparison represents the resolution.
In a brief description of the resolution, as illustrated in FIG. 6A, for example, in the case of a 10-bit A/D converter, an input voltage range from 0 V to 5 V is resolved into 1024 (the tenth power of two) levels of a reference voltage, and an input voltage is compared to the reference voltage to determine at which voltage level the input voltage is. In the case where the number of bits becomes greater, as illustrated in a 12-bit A/D converter of FIG. 6B, the input voltage range from 0 V to 5 V is resolved into 4096 (the twelfth power of two) levels of the reference voltage, and an input voltage is compared to the reference voltage to determine at which voltage level the input voltage is. That is, as the number of bits becomes greater, more detailed measurement of the input voltage can be carried out.
In general, in the case of detecting a potential difference in an input voltage, a differential amplifier includes an operational amplifier as a voltage value conversion circuit. The operational amplifier is used when a reference point of an input voltage A is not determined, for example, in the case of a battery voltage.
For example, when the polarity of an input voltage A1 is noninverting (i.e., always positive or negative), as illustrated in FIG. 7A, a gain (i.e., R2/R1) of a differential amplifier 151a is fixed, and (an input voltagexc3x97gain)=(A1xc3x97R2/R1)=(an output voltage B1), can be readily obtained by the differential amplifier 151, whereby a suitable output voltage B1 can be always output to an A/D converter in a next stage.
As illustrated in FIGS. 5 and 7B, when the polarity of an input voltage A2 is inverted in the process of sequentially storing the voltage values of the battery blocks 111 in the capacitor 130, by applying an offset voltage (DC 2.5 V) to a reference voltage for the differential amplifier 150, the input voltage range can be half the input voltage range of the A/D converter 160 (FIG. 5). Thus, it is possible to always output an output voltage B2 suitable to the input voltage range of the A/D converter 160 while the gain (i.e., R2/R1) of the differential amplifier 150 is fixed. That is, (an input voltagexc3x97gain)+(an offset voltage (DC 2.5 V))=(A2xc3x97R2/R1) +Voffset=(the output voltage B2), can be obtained by the differential amplifier 150.
In other words, as illustrated in FIG. 8A, when the polarity of the input voltage A2 is positive, an input voltage range from DC 2.5 V to the maximum voltage DC 5 V, which is half the input voltage range of the A/D converter 160, is used. When the polarity of the input voltage A2 is negative, an input voltage range from DC 2.5 V to the minimum voltage DC 0 V, which is half the input voltage range of the A/D converter 160, is used. Specifically, even when the A/D converter 160 is, for example, a 12-bit A/D converter, in practice, the A/D converter 160 can only have the input voltage range provided by an 11-bit A/D converter, whose resolution is lower than that of the 12-bit A/D converter.
As described above, in the conventional structure, in the case where the input voltage is voltage A1 of FIG. 8B having noninverting polarity, the entire input voltage range of the A/D converter 160 can be used, but in the case where the input voltage is voltage A2 of FIG. 8A having inverting polarity, only a half of the input voltage range of the A/D converter 160 can be used when the polarity of the input voltage A2 is positive, and the other half of the input voltage range of the A/D converter 160 can be used when the polarity of the input voltage A2 is negative, so that only half the full resolution of the A/D converter 160 is utilized.
According to one aspect of the present invention, a battery voltage measurement device includes: a plurality of first switching sections, in which each pair of adjacent first switching sections sequentially selects two output terminals of each of a plurality of battery blocks included in a battery pack; a level change section for changing a level of a battery voltage of each battery block which is input to the level change section via the first switching section; an A/D conversion section for performing an A/D conversion of battery voltage data output from the level change section; and a reference voltage control section for controlling an output of a reference voltage of the level change section according to the polarity of the voltage input to the level change section.
With the above-described structure, a reference voltage control section controls an output of a reference voltage for a level change section according to inverted polarity of a voltage input to the level change section, so that each time the polarity of a voltage is inverted, the input voltage from the level change section to an A/D converter can be in an input voltage range of the A/D converter. Thus, it is not necessary to restrictedly use only half the input voltage range of the A/D converter assigned to each of the opposite polarities as in a conventionally required manner, and the entire input voltage range of the A/D converter can be used, so that twice the resolution of a conventional A/D converter can be obtained, and the original resolution of the A/D converter can be entirely used.
According to one embodiment of the invention, the battery voltage measurement device may further include: a capacitance section for selectively storing a battery voltage of each of the battery blocks via the first switching section; and a second switching section for selectively applying the battery voltage stored in the capacitance section to the level change section, in which the level change section changes a level of the battery voltage stored in the capacitance section which is input to the level change section via the second switching section.
With the above described structure, when a battery voltage of each of battery blocks is stored in a capacitance section and then the battery voltage stored in the capacitance section is input to the level change section, each time the polarity of a voltage is inverted, the voltage input from the level change section to the A/D converter is caused to be in the input voltage range of the A/D converter, so that twice the resolution of a conventional A/D converter can be obtained, and an effect of the present invention such that the original resolution of the A/D converter can be entirely used can be attained.
According to another embodiment of the invention, the reference voltage control section may include: a third switching section for switching a reference voltage of the level change section; and a first switching control section for controlling the third switching section according to the polarity of the voltage input to the level change section. Alternatively, the reference voltage control section may include: a reference voltage generation section for generating a reference voltage for the level change section; and a reference voltage generation control section for controlling an output of the reference voltage generation section according to the polarity of the voltage input to the level change section.
With the above-described structure, in order to switch a reference voltage for the level change section so as to obtain twice the resolution of the A/D converter, switching of the third switch section is controlled according to the polarity of the voltage input to the level change section or an output of the reference voltage generation section is controlled according to the polarity of the voltage input to the level change section, whereby a required structure can be simple.
According to still another embodiment of the invention, the control performed in accordance with the polarity of the voltage input to the level change section may be performed based on prestored table information for switching control.
With the above-described structure, when the polarity of the voltage input to the level change section is previously known based on prestored table information for the switching control, the reference voltage control section controls the third switching section or the reference voltage generation section based on the table information for switching control, whereby the output of the reference voltage for the level change section can be readily controlled.
According to still another embodiment of the invention, when one preset reference voltage value is selected, if an A/D conversion output of the A/D conversion section represents a maximum value or a minimum value within an input voltage range of the A/D conversion section, the control performed in accordance with the polarity of the voltage input to the level change section may be performed so as to switch the one preset reference voltage value to the other preset reference voltage value.
With the above-described structure, in the case where the polarity of the voltage input to the level change section is previously unknown, when one reference voltage value is selected, if the reference voltage control section determines that an A/D conversion output of the A/D conversion section represents the maximum value or minimum value within the input voltage range of the A/D conversion section, the third switching section or the reference voltage generation section is controlled so as to switch the selected reference voltage value to the other reference voltage value, so that the reference voltage for the level change section can be readily controlled to be output in accordance with the polarity of the voltage input to the level change section.
According to still another embodiment of the invention, the battery voltage measurement device may further include: a fourth switching section for changing a feedback resistance value of the level change section so as to change a gain; and a second switching control section for controlling the fourth switching section according to the polarity of the voltage input to the level change section.
With the above-described structure, not only by causing the input voltage from the level change section to the A/D conversion section to be in the input voltage range of the A/D conversion section, but also by changing a gain of the level change section, the resolution of the A/D conversion section can be finer.
According to another aspect of the present invention, a battery voltage measurement device includes: a battery pack including a plurality of battery blocks; a plurality of first switching sections, in which each pair of adjacent first switching sections sequentially selects two output terminals of each of the plurality of battery blocks; a level change section for changing a level of a battery voltage of each battery block which is input to the level change section via the first switching section; an A/D conversion section for performing an A/D conversion of battery voltage data output from the level change section; and a reference voltage control section for controlling an output of a reference voltage of the level change section according to the polarity of the voltage input to the level change section.
According to one embodiment of the invention, the battery voltage measurement device may further include: a capacitance section for selectively storing a battery voltage of each of the battery blocks via the first switching section; and a second switching section for selectively applying the battery voltage stored in the capacitance section to the level change section, in which the level change section changes a level of the battery voltage stored in the capacitance section which is input to the level change section via the second switching section.
According to another embodiment of the invention, the reference voltage control section may include: a third switching section for switching a reference voltage of the level change section; and a first switching control section for controlling the third switching section according to the polarity of the voltage input to the level change section.
According to still another embodiment of the invention, the reference voltage control section may include: a reference voltage generation section for generating a reference voltage for the level change section; and a reference voltage generation control section for controlling an output of the reference voltage generation section according to the polarity of the voltage input to the level change section.
According to still another embodiment of the invention, the battery voltage measurement device may further include: a fourth switching section for changing a feedback resistance value of the level change section so as to change a gain; and a second switching control section for controlling the fourth switching section according to the polarity of the voltage input to the level change section.
According to still another embodiment of the invention, the reference voltage control section may include: a third switching section for switching a reference voltage of the level change section; and a first switching control section for controlling the third switching section according to the polarity of the voltage input to the level change section.
According to still another embodiment of the invention, the control performed in accordance with the polarity of the voltage input to the level change section may be performed based on prestored table information for switching control.
According to still another embodiment of the invention, when one preset reference voltage value is selected, if an A/D conversion output of the A/D conversion section represents a maximum value or a minimum value within an input voltage range of the A/D conversion section, the control performed in accordance with the polarity of the voltage input to the level change section may be performed so as to switch the one preset reference voltage value to the other preset reference voltage value.
Thus, the invention described herein makes possible the advantages of providing a battery voltage measurement device which can improve resolution using an entire input voltage range of an A/D converter even when the polarity of a voltage input to a differential amplifier is inverting.
These and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.